Electrostatic printer apparatus for printing with liquid ink



Sept. 4, 1962 R. M. SCHAFFERT 3,052,213

ELECTROSTATIC PRINTER APPARATUS FOR PRINTING WITH LIQUID INK Filed Dec. 17, 1958 2 Sheets-Sheet 1 INVENTOR 3 ROLAND M. SCHAFFERT Sept. 1962 R. M. SCHAFFERT 3,052,213

ELECTROSTATIC PRINTER APPARATUS FOR PRINTING WITH LIQUID INK Filed Dec. 17, 1958 2 Sheets-Sheet 2 VOLTAGE L+, H SOURCE VOLTAGE United States 3,052,213 ELECTROSTATIC PRINTER APPARATUS FOR PRINTING WITH LIQUID INK Roland M. Schalfert, Vestal, N.Y., assignor to International Business Machines Corporation, New York, N.Y., a corporation of New York Filed Dec. 17, 1958, Ser. No. 781,002 7 Claims. (Cl. 118-637) This invention pertains to an electrostatic printer apparatus and more particularly to an electrostatic printer apparatus for printing with liquid inks.

In general an electrostatic printer apparatus comprises an electrographic print element having a print surface, means for producing a latent electrostatic image in the form of a pattern of distributed electrostatic charge on said surface, development means for applying electrostatically charged particles of pigmented material to the print surface to render the latent image visible and transfer means for effecting the transposition of the visible image to a suitable print medium to which it may be aflixed. An electrostatic printer suitable for continuous print operation would include a print element having a continuous print surface in a form such as a drum or belt and means for moving the print element so as to cause successive increments of the print surface to be moved in sequence past the image production, the development, and the transfer apparatus. An example of a continuously operable electrostatic printer is shown in my U.S. Patent 2,576,047.

As is well known to persons skilled in this phase of the graphic arts, electrostatic images may be developed with either dry or liquid particles of electroscopic material. While liquid development of electrostatic images has held some promise for solving problems associated with transfer and fixing of dry electroscopic powders to a print medium, apparatus for liquid ink development has been complicated and cumbersome and has not been entirely satisfactory for commercial applications. This has been particularly true of liquid ink development apparatus which effects the development of electrostatic images through the generation of a gaseous suspension of charged particles in the form of a mist or spray from whence the particles are selectively deposited on the image bearing surface of the print element. This has been further especially true where this type of mist generating apparatus has been adapted for use in a continuous printer. Not only has control over the liquid particles in suspension been ineffective, but control over particle generation has been substantially lacking. Consequently, particle deposition occurs on surfaces other than image areas of the print element and contamination eventually results. Hence operative efficiency has been low since it has been necessary that more particles be generated than are expected to be available for selective deposition.

Therefore, it is a general object of this invention to provide an improved electrostatic printer for printing with liquid ink.

It is also an object of this invention to provide an electrostatic printer having an improved liquid ink development apparatus.

It is also an object of this invention to provide an improved liquid ink development apparatus having particular adaptability for use in a continuously operable electrostatic printer.

lI is a more specific object of this invention to provide a liquid ink development apparatus for use in anelectrostatic printer in which contamnation can be effectively eliminated.

It is a further specific object of this invention to provide a liquid ink development apparatus having increased con- 3,952,213 Patented Sept. 4, 1 $62 ice trol over the generation and deposition of the charged liquid ink particles.

It is a still further object of this invention to provide improved liquid development means which is simple in design as well as operation.

In general this invention is practiced to obtain the above as Well as other objects, further to be understood, by providing an electrostatic printer having an electrographic print element adapted to have a latent electrostatic image formed on a print surface thereof and development means located proximate to that surface, the development means being operable in response to the electrostatic image on the print surface for producing a spray of charged liquid ink particles proximate to that surface.

In a preferred more specific embodiment, there is provided in accordance with this invention a development means Which comprises electrode means positioned proximate the print surface and means for applying a fluid ink thereto. A voltage source connected to the electrode means and the print member establishes a biasing potential alterable by the potential of the electrostatic image for producing a corona discharge from the electrode means thereby generating a spray of charged liquid ink particles. A specific form of the electrode means of this invention comprises a plurality of conductive elements arranged in a row and extending transversely to the direction of motion of the print element. The conductive elements are designed to have pointed end portions located proximate the print surface with base portions in contact with a fluid ink supply. Capillary means formed in the conductive elements operate to ink the end portions thereof.

Another form of electrode means having particular suitability for use in a continuous printer but not necessarily limited thereto comprises a plurality of conductive elements radiating from a movable development member operable to successively immerse the conductive elements in a fluid supply and to transfer them to a location proximate the print surface. A voltage source connected to the development member and the print element establishes a biasing potential on the conductive elements which is alterable by the electrostatic image potential for the production of corona discharge from the conductive elements proximate the print surface.

In order to compensate for possible variations in the onset potential due to change in atmospheric conditions and other operating conditions, it is a feature of this invention to provide for the application of a biasing potential which is greater than the onset potential for producing corona discharge and a control bias potential applied to suppress the formation of corona at the electrode means which is alterable by the potential of the electrostatic image to produce corona discharge therefrom.

Thus it can be appreciated that an improved electrostatic print apparatus has been provided for printing with liquid inks. A development means operable in response to the electrostatic images for producing a liquid ink spray is inherently simple and efficient. In addition the possibility for contamination to occur has been greatly reduced since continuous mist or spray generation is eliminated. It will be further appreciated that an elecstatic printer has been provided in which liquid development of electrostatic images can be obtained without increasing the hazard of contamination notwithstanding continuous operation of the electrostatic printer. It is also believed clear an improved electrostatic printer has been provided in which liquid ink development may be conducted in a more efficient operation thereby extending the possibility for increased commercial application. Further advantages will be apparent from the following description, while the novel features of the invention are set forth with particularity in the appended claims.

Other objects of the invention will be pointed out in the following description and claims and illustrated in the accompanying drawings, which disclose, by way of examples, the principle of the invention and the best mode, which has been contemplated, of applying that principle.

In the drawings:

FIG. 1 is an isometric view showing a schematic embodiment of an electrostatic printer apparatus incorporating the features of the invention.

FIG. 2 is a graph illustrating the principles of the formation of corona from a pointed electrode located proximate a flat conductive plate.

FIG. 3 is an isometric view showing a second embodiment of an electrode means utilizable in the present invention.

FIG. 4 is a schematic view of an electrostatic printer designed for continuous printing operation incorporating another embodiment of the development means of the present invention.

FIG. 5 is a fragmentary view of the apparatus of FIG. 4 showing still another embodiment of the development means incorporating the features of the present invention.

FIG. 6 is an isometric view of the development means illustrated in FIG. 5 showing essential portions in crosssection.

FIG. 7 is a schematic diagram illustrating the further feature of the invention compensating for variation in the operating conditions associated with the function of the present invention.

Considering the present invention in more specific detail, reference is now made to FIG. 1 where an electrostatic printer is shown which comprises an electrographic print element 10 adapted to have a latent electrostatic image formed thereon by suitable means (not shown). Print element 10 is mounted in a suitable manner so as to be movable in a substantially horizontal plane, e.g., by a reciprocable rack 11 operably connected to motor 12 through gear 13 attached to shaft 14 thereof.

While print element 10 may be of any type capable of carrying an electrostatic image, it is preferably an electrophotographic plate having an upper layer 15, a photoconductive insulating material, such as amorphous selenium, superimposed on a canductive substrate 16 in accordance with well-known principles, layer serves as a carrier medium for electrostatic charges, and its upper surface serves as a print surface over which the development of images will take place to be ultimately reduced to printed copy form.

In accordance with this invention, electrostatic images, such as are illustrated at 17, are developed by selective deposition from a spray of charged liquid ink particles produced under the control of the latent image and proximate to the surface of layer 15. For that purpose a liquid development means 18 is mounted above the path of travel of and preferably coextensive with the width of print element 10. Located proximate the print surface of layer 15 are electrode means adapted to be operable in response to the existence of a latent image charge potential carried by said layer. In one preferred embodiment, the electrode means comprises a plurality of conductive elements, which may be copper wire for example, having pointed end portions 2% and arranged in a row across the path of travel of print element 111. Any suitable means for supplying fluid ink to the conductive elements 19 may be provided but in the form shown in Aft ductive elements 19 relative to container 21 may be made in any well-known manner such that fluid ink tends to flow downwardly over the surface of each of the elements to the pointed end portions 2%). In the preferred embodiment, however, each of the conductive elements has its outer surface etched to produce a wetting of the end portions by capillary action. Thus fluid ink flow is less likely to produce dripping or runoff from the pointed end portions 20 and yet will satisfactorily provide for an adequate supply of fluid ink for the production of a charged spray. In the event that more dense spray of fluid ink particles may be required, e.g., where it is desired to increase the speed of print element movement, a liquid spray development means may be provided as shown in FIG. 3. There a plurality of conductive elements 19, preferably of the same type as in FIG. 1, are arranged in a plurality of parallel rows extending downwardly from container 21 and transversely to the direction of motion of print element 11). If desired, a layer 23 of saturable material may be provided to limit gravity flow over the outer surface of conductive elements 19 so that inking of the end portions 20 occurs primarily through capillary action.

To attain image controlled generation of charged liquid ink particles, a biasing potential is applied to the electrode means which is alterable by the image potential to effect corona discharge from the inked end portions 20. For this purpose a voltage source 24 is provided which is connected to conductive elements 19 in any suitable manner and preferably by connection with container 21 with which the conductive elements may be in electrical contact. The second side of voltage source 24 may be connected to a common terminal 25 which is connected to substrate 16 and then to ground. In the event that images 17 are formed with positive charge, the negative side of voltage source 24 is connected to conductive elements 19. In the event the electrostatic images are of the opposite charge, the positive side of voltage source 24 would be connected to the conductive elements. Where it is desired that the same apparatus be usable for printing from images of either charge, suitable means, such as a switch (not shown), may be provided. In the preferred manner of practicing the invention, the voltage connection should be such that a negative corona will form from the ends of the conductive elements 19 and a latent image of appropriate charge polarity will be formed on print element 10. In either case however the bias potential applied to the conductive element is such that no corona will be produced except under the influence of the potential of the latent electrostatic image when it is brought within a predetermined distance from the end portions of the conductive elements.

For a better understanding of the nature of the principle involved, reference is made to FIG. 2 where a graph shows the variations in current flowing in a circuit which includes a pointed electrode spaced from a flat conductive plate to which a variable potential is applied. It will be seen from curve 26 that the application of voltage to the conductive element and flat plate produces a small current which increases at a relatively low rate as the potential is increased. The rate of current fiow increases sharply as the voltage approaches the point identified as V At this point corona will begin to form at the end of the pointed electrode, however, the corona formation is not yet selfsustaining. The precise point at which V occurs will depend on such factors as the sharpness of the point of the electrode, its separation from the surface of the conductive plate, air pressure, relative humidity, and to some degree the polarity of the potential being applied to the electrode. Further increases in the current are observed for a continued increase in the applied potential. The nonself-sustaining corona discharge condition continues until point V on the curve is reached. A continued increase in potential beyond the point of V ultimately produces breakdown across the gap causing arcing or sparking which is represented as the discontinuity on curve 27 identified as V Considering curve 26 once again, the potential represented by V is referred to as the starting or onset potential. It is the potential at which a self-sustaining corona discharge will be obtained. Hence in practicing the present invention, it is desirable that the bias potential applied to conductive elements be less than but proximate to the potential V and that the conductive elements 19 be spaced from print element In such that when image 17 is in the vicinity of end portions 20, the effective potential across the gap will be greater than the point V The operation of the invention in accordance with the apparatus embodied in FIG. 1 calls for the formation of an electrostatic image 17 on print element 10. The formation of the images may be accomplished while the element is mounted on rack 11 at a location to the right of the position shown or may be accomplished while element 10 is removed from its reciprocably mounted position on rack 11. The potential applied to the substrate 16 and electrodes 19 may be adjusted and a number of trial passes made to establish the conditions necessary to produce corona discharge in the presence of the image as it moves past the end portions 20. Having thus established the necessary operating conditions by one or more trial runs, succeeding runs may be obtained by merely moving the electrostatic print element one or more times along the path indicated by the arrow past the print elements to selectively alter the bias potential on certain of the elements to generate selectively a spray of ink particles which due to the close proximity to the surface of print element 10 is under the control of the image field from the time of generation. Similarly in connection with the electrode means of FIG. 3, the print element 10 is moved past the end portions 20. In the case of the plural row arrangement of electrode elements of FIG. 3, it is expected that a complete development of the electrostatic images could be obtained at higher speeds and possibly with a single pass of the print element relative to the electrodes.

An additional embodiment for producing a high density liquid spray in the vicinity of the print element surface may be seen by reference to FIG. 4. While the particular development means of FIG. 4 is shown in an electrostatic printer operable to print continuously, it is readily usable in other apparatus forms. In the schematic illustration of FIG. 4, a drum 28 is mounted on a shaft 29 which is suitably supported in a frame member (not shown) for rotation in a counterclockwise direction. Shaft 29 may be driven by suitable connection to an electric motor for example or other suitable means not shown. Drum 28 includes electrically conductive cylinder 30 on which a print element 31 is mounted. As in FIG. 1, the print element 31 comprises an insulating layer superimposed on a conductive substrate. In the present instance for convenience and ease in handling and attachment to cylinder 30, the conductive substrate is preferably flexible. The print element 31 is secured to cylinder 30 in any of the Ways for attaching a print plate to a support cylinder for example by suitable clamping devices. It is necessary that the substrate be in good electrical contact with the electrically grounded shaft.

In a manner well known to persons skilled in the art, sensitization, exposure, development, and transfer apparatus are located at radially spaced stations about the print element. Sensitization apparatus is preferably a corona discharge unit 32 adapted to apply electrostatic charge uniformly across the print surface of print element 31, The exposure apparatus for effecting the formation of a latent electrostatic image on the surface of print element 31 includes means for producing and projecting a photo-image of the material to be reproduced and may include lens 33. An illustrative type of transfer apparatus suitable for use with the present invention might include the print medium such as a paper in the form of the tape or web 34. Roll 35, perferably made of soft rubber to assure good contact, is suitably located to cause web 34 to contact the surface of print element 31 as it moves from supply roll 37 to a driven take-up reel 38. Reel 38 desirably may be connected to a common drive with the drum in such a maner as to effect the synchronization in drum peripheral speed and web travel.

Located intermediate the exposure and transfer stations is the development station which in accordance with this invention comprises an open tray 39 in which there is provided a supply of liquid ink 40. Located intermediate tray 39 and drum 28 is development member having a plurality of conductive elements 41 from which charged liquid ink particles are to be generated. In the preferred form conductive elements 41 are attached to a cylindrical drum 42 which in turn is mounted in electrical contact with and supported by a shaft 43. The development member may be connected to a drive mechanism in common with the drum 28 so as to produce a synchronous motion of the two relative to each other. However, the development member may have a separate drive which is adjustable so that the rate of motion of inked conductive elements past the moving surface of print element 31 can be separately controlled. In the embodiment illustrated, the direction of rotation of the development member is clockwise, and it may be desirable to rotate the development member at a speed greater than the peripheral speed of the print surface, thereby effecting a movement of the conductive elements past the moving print surface. The development member is positioned so as to extend into the open end of tray 39, whereby conductive elements 41 will, during the rotation of drum 42, be transported from a position of immersion in the fluid ink supply to the position proximate the print surface of print element 31. A voltage source 44 is connected so that a biasing potential may be applied to the conductive elements 41. For this purpose it is believed desirable that suitable connection can be made to shaft 43 and to shaft 29 of the drum 28.

A further embodiment of the development means suitable for generating liquid spray proximate the print surface is illustrated in FIG. 5 and FIG. 6. Conductive elements 45 take the form characteristic of a hypodermic needle. The conductive elements 45 are arranged in a row which is coextensive in length with the width of the print element 31. Each of the conductive elements may be mounted in a conductive base member 46 which is suitably mounted to be submerged in a supply of fluid ink 47 in an open tray 48. An inner capillary passage 49 formed in each of the conductive elements effects the conveyance of fluid ink to the pointed end portions 50. The converging surface of the capillary channel 49 of the conductive elements and the surface of the end portion form a sharp edge 51 from which corona discharge can form. While PEG. 5 illustrates the inner capillary construction in electrode means used in combination with the print element of the continuous type, it is to be understood that the same conductive elements may be provided in the embodiment of FIG. 1, as well as other embodiments, and particularly 'where it might be desirable to locate the development means below the path of travel of the electrographic print element on which electrostatic images are formed.

Referring to FIG. 7, there will be seen a circuit diagram illustrating an additional feature of the present invention. Since in practicing the invention in the embodimerits of the other figures, certain changes in construction or operating conditions can be expected to occur which might cause variation in the level of the onset potential needed to produce a corona discharge from the electrode means when they are subjected to the influence of the potential of the electrostatic image. To compensate for various conditions in accordance with this invention, a biasing potential will be applied to electrode means 19 from voltage source 24 which is greater than the onset potential V illustrated on the draft in FIG. 2.

To control the formation of corona so that none is formed unless an electrostatic image produces such formation, there is provided means for applying a suppressing potential intermediate the conductive elements 1.9 and print element It). The intermediate suppressing potential is preferably applied by a grid or other type electrode means located between the space separating conductive elements and the surface of print element 10 which is connected to a suitable voltage source 53. The voltage source 53 is preferably variable so that the potential applied thereto may be made adjustable under varying operating conditions. The potential applied to grid 52 will be such that the effective potential across the gap separating the grid and conductive elements is less than V shown on FIG. 2. However, the potential applied to 52 must be of a magnitude which when subject to the influence of the potential of the latent image 17, the effective potential at the tips of the pointed end portions 29 of conductive elements 19 will result in the generation of corona and a liquid ink spray of charged particles capable of being selectively deposited on the surface of print element 10 to develop the latent images 17.

While there have been shown and described and pointed out the fundamental novel features of the invention as applied to a preferred embodiment, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made 'by those skilled in the art, without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

1. In an apparatus for printing from electrostatic images, an electrographic print element having a print surface, development means for producing a liquid ink spray including electrode means positioned proximate said print surface, means for applying fluid ink to said electrode means, means for applying a bias potential across said electrode means and said print element, said potential being less than the potential for producing corona discharge from said electrode means, means for producing a latent electrostatic image on said print surface, said latent image having a potential for effecting corona discharge from said inked electrode means, and means for effecting a relative motion of said print surface past said electrode means.

2. An apparatus in accordance with claim 1 in which said electrode means comprises a plurality of conductive members arranged in a row across the path of travel of said print element surface, said conductive members being selectively operable across said row in accordance with charge potential on said print element surface.

3. In an apparatus for printing from electrostatic images, an electrographic print member having an image bearing surface, development means for producing a spray of liquid ink particles proximate said surface including means having a supply of fluid ink, a plurality of conductive members having pointed end portions located proximate said image bearing surface and base portions in contact with said fluid ink, said conductive members having capillary means for inking said pointed end portions, means for applying a biasing potential across said conductive members and said print element, said potential being proximate but less than the potential necessary for productive members has an inner capillary passage connect ing said fluid supply and said pointed end portion of said conductive member.

5. In an apparatus for printing from electrostatic images, an electrographic print member having a continuous print surface, means for moving said print member whereby said print surface passes along a predetermined continuous path, development means located adjacent said path for producing a gaseous suspension of charged liquid ink particles proximate said surface including container means for holding a supply of fluid ink and a development member having a plurality of radiating conductive elements, said development member being continuously movable to effect inking of successive conductive elements and transporting them to a position proximate said print surface, voltage means connected to said development means and said print member for applying a biasing potential across certain of said conductive elements proximate said surface, said biasing potential being less than the potential for producing corona discharge from said conductive elements nearest to said print surface, and means for producing a latent electrostatic image on said print surface, said image having a charge potential for effecting a self-sustaining corona discharge from said certain suc cessive ones of said inked conductive members moving proximate to said print surface.

6. In an apparatus for printing from electrostatic images, an electrographic print member having a print surface, development means for producing a spray of charged liquid ink particles including electrode means positioned proximate said print surface, means for applying fluid ink to said electrode means, means for applying a biasing potential across said electrode means and said print element, said biasing potential being greater than the onset potential for producing corona discharge from said electrode means, means for applying a control potential intermediate said electrode means and said print surface, said control potential being operable to suppress the formation of corona discharge from said electrode means, means for producing latent electrostatic images on said print element surface, said image having a charge potential for modifying said control potential for producing corona discharge at said electrode means, and means for effecting a relative motion of said print surface past said electrode means.

7. In an apparatus for printing from electrostatic images, an electrographic print element having a print surface, development means for producing a spray of charged liquid ink particles including first electrode means positioned proximate said print surface, means for applying fluid ink to said electrode means, means for applying a first potential across said electrode means in said print element, second electrode means intermediate said first electrode means and said print surface, means for applying a control potential to said second electrode means operable to suppress the formation of corona discharge from said first electrode means, and means for producing latent electrostatic images on said print surface, said images having a potential for modifying said second potential to produce corona discharge at said first electrode means.

References Cited in the file of this patent UNITED STATES PATENTS 2,451,288 Huebner Oct. 12, 1948 2,547,706 Huebner Apr. 3, 1951 2,556,550 Murray June 12, 1951 2,584,695 Good Feb. 5, 1952 2,586,047 Huebner Feb. 19, 1952 2,690,394 Carlson Sept. 28, 1954 2,784,109 Walkup Mar. 5, 1957 2,808,328 Jacob Oct. 1, 1957 2,824,813 Fauser etal Feb. 25, 1958 2,868,989 Haacke Jan. 13, 1959 2,878,120 Mayer et al Mar. 17, 1959 

